Spark plasma sintering and hot extrusion of aluminium alloy powder

The Spark Plasma Sintering (SPS) is a promising sintering technology to produce dense bulk pre-compacts from micro- or nano-structured aluminium alloys at lower temperatures and shorter sintering times. The densification behaviour and sintering response of an atomized Al-Si alloy sintered by SPS was investigated. A high density of bulk material with porosity less than 1 % can be prepared by SPS with a temperature of 450 deg C, holding for 2-5min and a pressure of 170 MPa. The particle size of the prealloyed powder influencing its electrical resistance plays a crucial role at the finding of the optimum processing parameters in case of a power-controlled sintering regime. In addition, the homogeneity of the microstructure across the diameter of the sintered samples are investigated and correlated with in-situ measurements of the temperature distribution within the samples. Residual porosity is mainly localised at the margin close to the wall of the die, corresponding to the lowest measured temperatures. The influence of the process parameters on the structure and tensile properties of subsequently hot extruded material was studied. The mechanical tensile properties of the SPSed compacts are significantly lower compared to that of the extruded material due to some residual porosity and the weakness of the joint between the initial atomized alloy powder particles. The extruded P/M material offers superior mechanical strength to the comparable compositions of known die cast piston alloys.